Toilet paper rolls (also called toilet rolls), as sanitary tissue paper rolls, are generally made by winding one sheet to three layers of sheets of sanitary tissue papers onto a paper core and into a roll (though there are products without paper cores). Usually, a roll made by winding one sheet of sanitary tissue paper is called one-ply, a roll made by winding two-layered sheets of sanitary tissue papers is called a two-ply, and a roll made by winding three-layered sheets of sanitary tissue papers is called a three-ply.
Particularly, in a case of toilet paper rolls made of 100% natural pulp, embossing is applied to the sanitary tissue paper to provide a thickness feeling and bulk softness. In a toilet paper roll made of such pulp, usually, about 60 m of sanitary tissue paper for one-ply, and about 30 m for two-ply, is wound onto a paper core having an inner diameter of 45 mm and a thickness of 0.5 mm, and made into a roll having about an 110 mm outer diameter. Recently, there are rolls called compact rolls in which 90 m for one-ply and 45 m for two-ply is wound around a paper core having an outer diameter of about 38 mm.
In such toilet paper rolls, since the toilet paper comes directly into contact with sensitive skin, rigorousness in quality is required from a consumer. That is, these products are always exposed to a consumer's rigorous selection, and thus, there are several high hurdles to be overcome in order for these products to be used.
A first hurdle is to provide a good image upon purchasing so that the product will be tried once. A second hurdle is not to disappoint the above-mentioned image, i.e., a consumer's expectations, upon actual usage.
(A) Object of Toilet Paper Roll in Order to Overcome the First Hurdle
Toilet paper rolls are usually displayed and sold in stores in packages wherein a plurality of toilet paper rolls are packed. It is thought that a consumer decides whether or not to purchase the rolls by holding the toilet paper roll in his/her hand, and by unconsciously imagining a feeling of the toilet paper upon use, based on the feeling upon holding.
Through this fact, the present applicant found that the feeling upon holding the toilet paper roll, that is, hardness felt upon holding the roll, becomes a potential purchasing index for deciding whether or not to purchase the roll. It is thought that purchasing is decided based on the thought that, for example, if the toilet paper roll feels hard upon holding the roll, the paper may be hard and uncomfortable upon usage in the form of a sheet in an unwound actual usage state, or, if the roll is too soft, the paper may rip upon usage because it is too soft also in the form of a sheet.
However, roll hardness of toilet paper rolls currently put on the market does not possess a suitable tender-touch. Thus, it is inferred that there are many cases where the rolls are losing an opportunity of being tried.
(B) Object Upon Giving the Toilet Paper Roll a Suitable Roll Hardness
On the other hand, in order to provide the roll hardness with a suitable tender-touch, there are the following objects. That is, conventional sanitary tissue paper rolls were either wound too hard and had poor thickness feeling or bulk softness, or on the contrary, wound too loose and the rolls easily deformed in a telescopic manner in which a central portion projects from sides, or their section deformed into a polygonal shape, and was poor in massiveness when holding in a hand.
Particularly, in a case where the roll was wound hard, although it is thought that by applying the above-mentioned embossing, the thickness feeling and bulk softness can be improved, only by providing clear embosses, an emboss is stretched and flattened and the thickness feeling and bulk softness are lost upon winding or as time passes due to tension in a winding direction. Further, in case of forming a compact roll, since sanitary tissue paper is wound around a core while being tensioned, an emboss is stretched and flattened due to this tension. Thus, it is not possible to enhance a thickness feeling and bulk softness.
On the other hand, if the paper is softly wound merely by lowering tension upon winding, windings tend to easily loosen. This not only becomes a cause of defectively wound items and deteriorates massiveness, but also causes a problem in that a roll diameter becomes too large even though a roll length is short. Particularly, if winding is performed with a usual roll length after providing clear embosses to increase paper thickness, even though flattening of the embosses can be prevented, the roll diameter becomes too large and the rolls cannot be held by usual holders.
(C) Object of Sanitary Tissue Paper for Toilet Paper Roll in Order to Overcome the Second Hurdle
Upon unwinding and actually using the toilet paper roll having been purchased mainly by image as explained above, it is necessary not to give an impression to a consumer, who purchased the roll, that he has been betrayed of his/her expectations. Further, upon use, the consumer will sensually evaluate, for example, a tender-touch, pliantness, bulk softness, hardness, and smoothness of the roll in a state of a sanitary tissue paper having been unwound from the toilet paper roll.
Therefore, conventionally, in addition to paper-quality data such as grammage, paper thickness, strength, and elongation which are generally-measured physical properties of paper, it has been typical for a manufacturer to adopt indexes such as “softness” or “MMD” as evaluation criteria corresponding to such sensory evaluation.
“Softness” shows a resistance value (average value in longitudinal and lateral directions) when pushing a paper, being 10 cm wide, into a 5.0 mm gap using a terminal. “MMD” shows a variation (average deviation) in a friction coefficient between paper and a contactor wound with a piano wire. These are measuring methods used generally for sanitary papers.
However, “softness” is affected by friction between the paper and the terminal, and does not always sufficiently correspond to tender-touch and/or pliantness evaluated by a person. Further, although “MMD” has a relationship with smoothness felt by skin, this resulting value has not been able to show a difference between a mere slippery feeling and smoothness.
Therefore, it has not been able to sufficiently grasp bulk softness, pliantness, tender-touch and/or smoothness to the touch, which are required for toilet papers, and thus, it was not possible to reproduce quality nor confirm that quality has been reproduced.
Only by paper-quality data, softness and MMD, a delicate quality felt by a person was not sufficiently grasped, nor was it possible to sufficiently conduct an absolute evaluation in a time series or a differential analysis compared with competitive products made by other companies.